Embedded FBG Sensors for Structural Health Monitoring of Advanced Composite Structures. Joshua Peauril B.Eng, B.Design

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1 University of Southern Queensland Faculty of Health, Engineering and Sciences Embedded FBG Sensors for Structural Health Monitoring of Advanced Composite Structures A Thesis submitted by Joshua Peauril B.Eng, B.Design In fulfilment of the requirements of Master of Engineering Research 2014

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3 ABSTRACT Fibre reinforced polymer composite materials (FRP) have been used in critical civil infrastructure for several decades due to their attractive strength to weight ratio and ease of manufacturing to meet required design objectives. However, the long-term behaviour of FRP structures is not well understood and the fear of catastrophic failure inhibits the wide-spread use of them. Frequent monitoring, therefore, is essential in order to know the structural integrity and damage status of the structure to give early warning signs. Recent developments in sensor technologies have significantly contributed to the improved health monitoring systems for critical infrastructure. Among those new generation sensors, Fibre Bragg Grating (FBG) sensors have demonstrated their superior properties in Structural Health Monitoring (SHM) of composite structures. This thesis details a conceptual design and application of an embedded FBG sensor network in a representative FRP bridge deck structure and a representative hybrid FRP bridge beam. Sensor embedding methods were developed that save production time and improved the durability of the sensors. The smart deck was tested under Uniformly Distributed Loads (UDL) with increasing simulated damage to show the FBG sensor ability to detect damage. The smart bridge beam was tested under cyclical four point bending and successfully showed FBG sensor ability to detect early signs of fatigue. Keywords: fibre Bragg grating, structural health monitoring, fibre composite, infrastructure, damage, fatigue i

4 List of Publications during this study Peauril, J, Epaarachchi, J, Wang, H, Lau, K.T., 2013, Embedded Fibre Optic Sensors under Multi-axial Loading, International Conference on Smart Materials and Nanotechnology, Gold Coast. Ku, H, Peauril, J, Cardona, F, Trada, M, 2014, Recycling Glass Fibre Composites Process and Viability, Journal of Polymer Science. (on review) Peauril, J, Watt, N, 2014, Lightweight Fibre Composite Bridges: Pedestrian and Road Applications, 6 th Australian Small Bridges Conference, Sydney. Peauril, J, Watt, N, 2014, Lightweight Composite Bridges and Decking Applications, Research to Reality: Promoting fibre composites in civil infrastructure, USQ, Toowoomba. Peauril, J, Epaarachchi, J, Wang, H, 2014, Smart FRP Bridge Deck Concept with Embedded Fibre Optic Sensors for Structural Health Monitoring, Composite Structures (submitted) ii

5 Certification of Dissertation I certify that the ideas, designs and experimental work, results, analyses and conclusions set out in this dissertation are entirely my own effort, except where otherwise indicated and acknowledged. The work is original and has not been previously submitted for assessment in any other course or institution, except where specifically stated. Signed: Date: Joshua Peauril Student ID: Endorsement by Supervisors Signed: Date: Dr. Jayantha Epaarachchi Principle Supervisor Signed: Date: Prof. Hao Wang Associate Supervisor iii

6 Acknowledgments I would like to thank those who have helped with the research both officially and unofficially: Dr Jayantha Epaarachchi, Prof Hao Wang and Dr Francisco Cardona for academic advice, Wayne Crowell and Mohan Trada for assistance with testing and technical issues and all of the composites centre (CEEFC) staff and students for their assistance on a daily basis. Special thanks goes to my wife and family, for without their love and support this achievement would not be possible. Joshua Peauril iv

7 Notation Abbreviatio n Roman Letters CFRP COV E FBG FRP GFRP L M MSE R SHM S.G. UDL V VARTM VE VIP or RIP Greek Letters δ ε Λ λ Meaning Carbon fibre reinforced polymer Coefficient of Variance Elastic modulus or Young s Modulus Fibre Bragg grating Fibre reinforced polymer Glass fibre reinforced polymer length moment Mean Squared Error Radius of curvature Structural health monitoring Specific gravity Uniformly distributed load Shear force Vacuum assisted resin transfer moulding Vinyl Ester polymer Vacuum infusion process/resin infusion process Deflection or deformation strain Aperture length Wavelength μ Micro (x10-6 ) σ Tensile stress τ Shear stress ϴ Angle theta Other Approximately equal to v

8 Contents ABSTRACT i List of Publications during this study ii Certification of Dissertation iii Endorsement by Supervisors iii Acknowledgments iv Notation v Contents vi 1. INTRODUCTION Background Aims Outline of the report 2 2. LITERATURE REVIEW Fibre Composites Overview of Composite industry growing applications in civil infrastructure FRP Infrastructure Design Approach Fibre Composite Material Properties Structural Health Monitoring (SHM) SHM of Composite Structures FBG Theory and measurements Embedding FBG Summary EXPERIMENTATION & ANALYSIS Introduction Experimentation of Sensor Embedding Methods in FRP Sensor placement and Securing Placing Sensor in Fabric Layers Ingress/Egress Treatment Vacuum Infusion Sensor Embedding Method FRP Deck Concept with Embedded FBG Finite Element Analysis (FEA) of Deck Deck Load Testing Optical Signal Processing Damage Detection in FRP Bridge Decking using FBG Sensors Hybrid FRP Beam Concept with Embedded FBG Hybrid FRP Beam Design Finite Element Analysis of Hybrid Beam Manufacture of Beam with Embedded Sensors Cyclic Testing of Beam Summary 33 vi

9 4. DATA ANALYSIS Strain Normalising Power Range Peak Detection Spectrum Indicators Spectrum Shape Factor and FWHM Gradient of Line of Symmetry Summary RESULTS AND DISCUSSION Deck Test Results Simply Supported UDL Distortion Indexes Damage Detection in Deck Beam Results FBG Response Summary SUMMARY AND CONCLUSION Summary of Findings Implications Further research Conclusion 50 References 51 Appendix A: List of Figures 53 Appendix B: List of Tables 56 Appendix C: Production Drawing 57 Appendix D: FEA Plots 58 vii

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